Twin-cylinder constant speed hydraulic system



April w. R. TUCKER 1 2,374,630

TWIN -CYLINDER CONSTANT SPEED HYDRAULIC SYSTEM Filed Jan 23, 1945 INVENTOR WARREN R TUCKER ATTORNEY Patented Apr. 24, 1945.

TWIN-CYLINDER CONSTANT SPEED HYDRAULIC SYSTEM Warren It. Tucker, Dayton, Ohio, assignor to The Hydraulic Development Corp., Ine., Wilmington, Del., a corporation of Delaware Application January 23, 1943, Serial No. 473,336

9 Claims. (Cl. 6097) This invention relates to hydraulic machinery and, in particular, to a control system for a plurality of hydraulic motors.

When a plurality of hydraulic motors is supplied with pressure fluid from a common fluid source, the motor encountering the lowest resistance tends to run ahead of the other motor or motors, which will either move in an erratic manner or may even come to a stop.

It is an-object of this invention to provide a hydraulic motor control system which will overcome the above mentioned drawback.

' It is another object of this invention to provide a hydraulic system including a plurality of fluid operable motors supplied with pressure fluid from a common fluid source, in which a change in retically no eifect on the speed of another motor of said system.

It is another object of this invention to provide a hydraulic system including a plurality of fluid operable motors supplied with pressure fluid from a common fluid source, in which control means is provided adapted. automatically to maintain the speed of each individual motor substantially constant.

Another object of this invention consists in the.

Itisa still further object to provide a hydraulic system including two fluid operable motors supplied'with pressure fluid from one and the same sistance, encountered by one motor will have prac- These and. other objects and advantages of the invention will appear more clearly from the following specification in connection with the accompanying drawing which illustrates, by way of example, an embodiment of the new control system.

The control system shown in the drawing comprises in general two hydraulic motors supplied with pressure fluid from a common variable delivery source, and being hydraulically connected with a balancing valve. The balancing valve, in its turn, is connected with means for creating back pressure in said motors, and is also in fluid communication with a control mechanism associated with the fluid source feeding said motors. The said control mechanism is pressure responsive and adapted to vary the supply of pressure fluid to said motors.

A variation in resistance encountered by one of said motors reacts on said balancing valve so as to cause the latter to create back pressure on the motor encountering the least resistance to such an extent as to exactly balance its load a with that of the motor of higher resistance. In

fluid source, in which means are provided for maintaining adesired back pressure at said moa decrease in resistance encountered b one of said motors, the supply of actuating fluid to one motor is increased or decreased respectively, while the speed of the other'motor is maintained substantially constant.

' tors, and in which, responsive to an increase or side of the pump I, while the conduit l1 communi addition thereto, the delivery of fluid from said fluid source to said motors is changed. Then a new pressure condition prevails because the pressure created by the fluidsource stands on both I determined by the greater 'mo.

structure shown therein comprisesfa pumpfl of i the variable deliverytypawhichmay be a radial] piston or radial vane pump. .The flow control member of the pump I hasieonnectedtheretoa control rod 'lwith a piston 3, whichlatter is re ciprocably mounted in a servomotor cylinder 4.

The flow control memberof the pumpl is. con

tinuously urged, by means of aspring [in 2, cas-,

ing 6, in a direction to move the pump into increased delivery position.v The casing 8 is con nected to the pump I in anyconvenient manner.

The suction side of the pump is connected by means of a conduit 1 with a fluid reservoir or tank 8. Also connected with the,tank 8 is a conduit 9 leading to the port l0 in the four-way valve I I. The four-way valve II is also provided with ports l2, l3 and I4 respectively connectedwith conduits l5, l6 and I1.

- The conduit I6 is" connected with the pressure cates with theupper portion of the cylinders l8 and I9. Reciprocably mounted in the cylinders l8 and I9 respectively are plungers 20' and 2t.

' The lower portion 01' the cylinder 18 communicates through a conduit 22 with a conduit 23, which latter comprises a check valve 24 and has 'one end connected to the conduit l5, while the other end leads to an annular recess 25 in the valve casing 26 of a balancing valve, generally designated 21.

Reciprocably mounted in the valve casing 26 is a valve'member 26 having three s aced and interconnected piston portions 29, 36 and 3 I. The

left end of the valve casing 26 is connected through the conduit 32 with a conduit 33, which latter leads to the servomotor cylinder 4. The space intermediate the piston portions 29 and 336 communicates with a conduit 34 comprising a choke valve 35 and leading to the conduit l5.

annular recess 39 communicating through a conduit 46 with the conduit l5, which latter comprises a check valve 4| and is in fluid connection with the lower portion of the cylinder l9.

, Operation It may bexassumed that the pump I has been started and that the valve cock 42 has been moved into the position shown in the drawing, in which is establishes fluid connection between the conduits l6 and I1. I pump -I will then pass through the conduits l6 and I1 into the cylinders l6 and I9, where it will act upon the plungers 26 and 2| respectively so as to move the same downwardly.

Fluid expelled from the lower portion of the cylinder I6 passes through conduits 22 and 23 .intO the recess 25 in the valve casing 26, and

from there will flow through the conduit 34, choke valve and conduits l5 and 9 into the tank 9.

Due to the choke valve 35, a back pressure will be established in the conduit 34' between the choke valve 35 and the valve casin 26. This pressure will be conveyed through the conduit 32 into the left hand portion of the valve casing 26 and will be conveyed also through the conduit 43 into the servomotor cylinder 4.

The fluid expelled from the lower portion of the cylinder I 9 passes through the conduits l5 and 46 into the recess 39 of the valve casing 26,

and from there through the conduit 36, chock valve 31 and the conduits 5 and 9 into the i tank 8.

come unbalanced, and that the load on the plunger 26 increases. will slowdown and the pressure in conduits 22 and 23 will drop somewhat. Therefore, also the pressure on the right side of the piston portion 29 and in conduits 34 and 32, as well as the p ssure acting on the left side of the piston portion 29, will dropv Consequently, the valve member 28 wlli move towardthe left, increasing th free communication between the conduit .23 and the recess 25, while decreasing the free communication between the conduit 46 and the recess 39. Due to the increase in the free communication between the conduit 23'and the recess 25, the back pressure in the conduit 22 and thereby the resistance encountered by the plunger 26 will decrease so that the pressure load on the plunger 26 is substantially restored.

The decrease of the free communication between the conduit 46 and the recess 39 results in a higher back pressure in the conduits 46 and |5 and, therefore, in a greater load acting on the plunger 2|. Without further control mechanism, the plunger 2| would slow down. However, since the decrease in pressure in the conduit 34 was also conveyed throug-hthe conduit 43 into the servomotor cylinder 4, the spring 5 has shifted the Pressure fluid delivered by the 7 31 and the valve casing 26, which pressure will be conveyed into the right hand portion of the valve casing 26 through the conduit 38.

The differential pressures respectively acting upon the p ston portions 29 and 3| move the valve member 26 into a position in which these pressures balance each other. It may be assumed that a when the said pressures balance each other, the

valve member 28 occupies the position shown in Unbalanced motor loads It may now be assumed that, for some reason, the loads acting on the plungers 26 and 2| beflow control member of the pump into a new positionin which the delivery of the pump I is increased. The increase in delivery of the pump goes to the cylinder l9 and makes up for the increased resistance encountered by the plunger 2|, so that the speed of the plunger 2| remains substant ally the same, in spite of the new bal- Y ancing position occupied by the valve member 26.

In other words, the speed or both plungers 26 and 2| is substantially maintained, in spite of variations in the load encountered by these plungers.

If the load on the plunger 26 had decreased instead of increased, as described above, a similar series of operations would have been effected, but these operations would have been exactly reverse to those set forth above.

If, for some reason, it should now happen that theload on the plunger 2| increases, the control operation is efiected in a somewhat different manner, due to the fact that the control pressures in the conduit 36 do not act directly upon the servo motor 3, 4. An increase in load on the plunger 2| will first 'slow down the latter. This in turn will bring about a decrease in pressure in the conduits l5 and 46 and, thereby, also in the recess 39 and the conduits 36 and 38. In this way, the balance on the valve member 28 is disturbed and the valve the recess 25 is decreased, while the free communication between the conduit 46 and the recess 39 is increased. The decrease in the free communication between the conduit 23 and the recess 25 results in a slight pressure drop in the cone duits 34 and 33 and, therefore, also results in a pressure drop in the right hand end of the servomotor cylinder 4. Therefore, the spring 5 moves the pump into an increased delivery position.

A greater quantity of fluid is, therefore, delivered by the pump I through the conduit f|| into the cylinder I8, which makes up for. the increased load on the plunger 26 created by the decrease in free communication between the conduit 23 and the recess 25. Another part of the increased delivery of fiuid by the pump enters the cylinder I9 and makes up for the increased load acting on the plunger 2|, In this way, the speed of the plungers As a result thereof, the plunger 26 2| II is substantially maintained in spite of the change in load acting thereupon;

Again the same sequence of actions would occur with opposite effects if a decrease'rathel' than an i is made up by the increased delivery or the pump increase oi load were eilected upon the plunger 2 i. Change in the throttle setting It may now be assumed that the operator desires to change the speed of one plunger, for

instance, wants to increase the speed of the plunger 23. To this end, the operator opens the choke valve 35 and sets the same in correspondence ,to the desired speed. As a result of the new setting of the valve 33, the pressure in conduits v 33 and 33 falls oi! slightly, This in turn results in' a pressure drop in the right hand portion of the cylinder I so that the spring I moves the pump t into an increased delivery position.

and, thereby, also in the left hand end of the valve casing 23 causes the valve member 23 to move toward the left. Consequently, the free communication between the conduit 23 and therecess 23 is increased; while the free communication between the conduit Iii and the recess 39 is decreased. Due to-.this increase in free communication between the conduit 23 and the recess 25, the pressure in the conduits 22 and. 23, drops and the plunger moves faster. The restriction of the free communication between the conduit) and the recess 38 results inan increased pressure in the conduit I3, and. thereby in an increased load acting on the plunger 2|. Under normal circumstances, this would result in a slow down of the j plunger 2l.- However, since the pump I has been shifted into an increased delivery posit on as mentioned above, an increased quantity of fluid is delivered by the pump into the cylind r i9. making up for the increase in load on the plunger 2| so that the plunger 2i substantially maintains its speed while the plunger 20 now moves at in-.

creased speed, as desired.

It will be obvious that acorresponding control operation will be effected it the operator adjusts the choke valve 33 to bring about a reduction in speed 01' the plunger 20.

Ii'it is now desiredto increase the speed of the plunger 2|, the control operation diiters somewhat from that described above in connection with the setting oi the 'ch'okavalve .33 becaus'e the the pressure in the conduit 33 drops slightly and,

consequently, also a pressure drop occurs in the recess 31' and the conduits 36 and 38 as well as in the right hand end of the valve casing 25. Therefore; thebalance acting on the valve member 28 co the flow oi fluid from said-outlets toan exha s i disturbed and the valve member 23' moves to t ward theright. This movement reduces the free communication between therconddit 23-and the recess 23, while increasing the free communication between the conduit 40 and the recess. The decrease in tree communication betwcen the conduit "and the recess 23 brings about a drop 'in pressure in the conduits 34, 32 and '33 and, thereiore, alsoih t e right hand end. portion of the servomotor cy nder I. Consequently, the spring 5 moves the pump i into increased deliveryposition until; the thrust, exerted by the sp n balanced by the pressure acting on the larger area oi' the piston 3. i

The decreasein free communication between creased load on the plunger 23 and would normally slow down the speed of the'plunser 23. However, this increase in load on the plunger 23 'l into the cylinder I3 so that the speed oi the plunger 23 remains substantially constant. Since, on the other, hand, the free communication between the conduit 43 and the recess 33 has been 1 increased, a pressure drop occurs in the conduit it so that the load on the plunger 2i is decreased and the speed of the plunger 2| is increased as desired.

It it is desired to decrease the speed or the plunger 2i instead of increasing the speed, it is obvious that the valve 31, instead of being opened, will be further closed, whereupon the control operations will then occur inan order reverse to that Just described for increasing the speed of the 20 plunger 21.

. When it is desired to reverse the movement of the, plungers 20 and II, the operator reverses the valve cock 42 so as to establish fluid connection between the conduit i1 and the conduit 8, while 25 simultaneously connecting the conduits l3 and it ,with each other. It will then be clear that pres.-

' sure fluid delivered by the pump i into the conduit so cylinder i8, and will also flow through the check valveli into the lower portion of the cylinder IS; The plungers 20 and 2! will then move upwardly. and thefluid expelled thereby will flow through the conduits l1 and 3 into the tank 3:

r In the control system shown in the drawing, the return speed of the plungers 20 and 2| is not controlled by the valve 21 so that the full delivery of the pump i is conveyed to the lower portion of the cylinders and I9.

w While the invention has been described in connection with reciprocable plungers 20 and 2i, it

. will be obvious that the control system would work equally well with rotary motors without requiring any change in the system.

45 It-will be understood that the invention is not,

limited to the particular structure shown inthe drawing, but also embracessuch modifications as, come within the scope-of the claims,

Having thus fully described myinvention, what I claim as new and desire to secure by Letters Patent, is: I g

1. In a hydraulic system, a plurality of fluid operable motors, each motor having'a fiuid'inlet and a restricted fluid outlet, a fluid source com- .mon tosaid motors for supplying pressurefluid to said inlets to actuate said motors, means for establishing fluid connection between said fluid source and said inlets, pressure responsive control means associated with said outlets .for controlling saidcontrol means being operable to simultaneously vary the restrictions in said outlets in re-. sponse and according to changes in loads on said motors, and means operatively connected with tioned means 'being adapted to maintain the speeds of said motorssubstantially constant.

2. In -a hydraulic system, a plurality'ot hydraulic motors with fluid inlets and out1ets,the

inlets or said motors being hydraulically interconnected during the movement of said motors in' 7 one direction, a' fluid source of variable delivery *f I 3 tne'eon uit'z'sand the recess It results in. mm

4 for supplying pressure fluid to said motors to actuate the same, means for selectively conveying pressure fluid from said fluid source to said motors, and control means operatively connected with said motors and said fluid source for automatically varying. the supply of pressure fluid from said fluid source to said motors and the rate of fluid flow through each of said motors in reconveying pressure fluid from said fluid source to said inlets, choke means for maintaining pressure at the outlets of said motors, valve means interposed between said outlets and said choke means for controlling the flow of fluid from' said outlets to said choke means, said valve means being operable in response to a variation in pressure between said valve means and one of said choke .means for varying the flow of fluid from the outlet of one motor to the choke means pertaining thereto in an inverse order to the variation in the flow of fluid from the outlet of another motor to the choke means pertaining thereto, and means associated with said fluid source for varying the supply of fluid from said fluid source to said m0- tors in accordance with the operaton of said valve means to thereby. maintain the speed of each individual motor substantially constant.

4, In a hydraulic system, a pair of fluid operable motors having their inlets continuously interconnected during the movement of said motors in one direction, means for supplying pressure fluid to said inlets for actuating said motors, a plurality of choke means respectively associated with said fluid operable motors, valve means interposed between the outlets' of said motors and said choke means and adapted in response to variations in pressure at the outlet of one motor to vary the pressure at the outlet of the other motor, and control means associated with sat'd fluid source and responsive to the actuation of .said valve means for bringing about a change in the quantity of fluid delivered from said fluid source to said motors to thereby maintain the speed of said motors substantially constant.

5. In a hydraulic system, a pair of hydraulic motors with a fluid inlet and outlet for each motor, a fluid source common to each of said motors for supplying pressure fluid thereto toactuate said motors, a plurality of choke means respectively associated with the outlets ofsaid motors for maintaining pressure at saidoutlets.

a reciprocable valve member for controlling the flow of fluid from said outlets to said choke means, piston means associated with said valve member and operable in response to variations in pressure at each of said outlets to thereby actuate said valve member for restricting the flow of fluid of one of said motors, while simultaneously bringing about an increase in the flow oi fluid at the exhaust of another motor to the choke means pertaining thereto, and control means operatively connected with said valve member and said fluid source for varying the supply of fluid from said fluid source to said motors to maintain the speed of said motors substantially constant.

6. In a hydraulic system, a plurality of hydraulic motors with an inlet and an outlet for each motor, a fluid source of variable delivery for supplying pressure fluid to said motors, control means for controlling the delivery of said fluid source, means for simultaneously connecting said fluid source with each of said inlets, a plurality of choke means respectively associated with said outlets for maintaining pressure at said outlets, and pressure responsive means interposed between said outlets and said choke means and adapted in response to variations in pressure at one of said choke means to bring about a corresponding change in pressure at another choke means and also to actuate said control means for a variation in the delivery of said fluid source so as to maintain the speed of said motors substantially constant.

the combination with said motors of a variable delivery source of fluid pressure for supplyingpressure fluid thereto, valve means for selectively establishing fluid connection between said fluid source and the inlets of said motors, flow responmotors.

sive means in the outlets of each of-said motors for creating control pressures therein, means associated with said fluid source for varying the delivery thereof in response to one of said control source of fluid pressure for supplying actuating fluid thereto, flow responsive means in the outlets o'f each of said motors for creating control pressures therein, means for controlling the supply of fluid from' said fluid source to said motors in response to at least one of said control pressures, and flow restricting means adapted in response to both of said control pressure tocontrol, the rate of fluid flow through each of said motors.

9. In a fluid operable system for simultaneously operating a pair of fluid operable motors at substantially constant and mutually independent speeds, the combination with said motors of a source of fluid pressure for supplying actuating fluid thereto, flow control means operable to vary the supply of fluid from said source to said motors,

other flow control means operable to control the WARREN R. TUCKER, 

